1. Field of the Invention
The present invention relates to an image forming apparatus that forms an image on an image receiving medium, for example, a color copier, monochrome copier and so on.
2. Description of Prior Art
In recent years, along with wide use of color documents in offices, color copiers have been widely put on markets. As one of these color copiers, there is a 4-drum tandem type. In this type, four photosensitive drums as image carriers are arranged in parallel, and toners of yellow, magenta, cyan, and black are used on the respective photosensitive drums to form toner images. These toner images are transferred one by one onto a sheet of image receiving medium that is carried on a conveyor belt, and thereby a color image is obtained.
In these color copiers, color displacement among four colors affects largely upon image quality. One of the causes for this color displacement is snaking of a conveyor belt.
To prevent this snaking of conveyor belt, a regulation plate is arranged in parallel with the conveyor belt at the end of front side of a driving roller of the conveyor belt. When the conveyor belt runs, the end edge thereof is slid on the plate surface (sliding surface) of the regulation plate and thereby guided.
However, in the conventional regulating method, the conveyor belt may run over the regulation plate. As countermeasures against the above, the area of the regulation plate is made wide, but when the area of the regulation plate is set wide, the area occupied by the regulation plate itself becomes large, as a result the copier itself becomes large, which has been a problem with the prior art.
And, when the lay force of the conveyor belt that slides on the regulation plate is large, the conveyor belt may temporarily twist up on the sliding surface with the regulation plate. If this twisting up status continues, bending fatigue occurs near the root of the twisting up of the conveyor belt and the conveyor belt is broken, which has been another problem with the prior art.
The problem of breakage of the conveyor belt owing to bending fatigue cannot be solved by merely making the regulation plate large.
As mentioned above, the conventional method by regulation plate has had the problem of the occupied area of the regulation plate and the problem of belt bending fatigue.
While, belt snaking amount is determined by the surface roughness of the sliding surface of the regulation plate, and the straightness of the end edge of the conveyor belt that slides on the sliding surface of the regulation plate. However, in the prior art, there has not been any standard as to how the surface roughness of the sliding surface of the regulation plate and the straightness of the end edge of the conveyor belt should be set.
And also the rigidity relation among the conveyor belt and the regulation plate and a supporting component that keeps the regulation plate has not been clearly specified.
Further, when lay force works large on the conveyor belt owing to external disturbance or so, total lay force works upon the regulation plate and the conveyor belt may be broken.